1. Field of the Invention
This invention relates to instruments for locating and following underground pipes, cables, and other underground entities which have electrical continuity, whether inherent naturally therein or intentionally associated therewith.
2. Description of Related Art
It is well known to locate underground utilities, such as electrical cables, water mains, and gas pipes, by imposing an electromagnetic signal thereon and detecting the magnetic field generated by the current flow therethrough. Non-conductive underground utilities, such as fiber optic cables, are commonly provided along their entire length with either an electrically conductive sheath or an electrically conductive lead intimately associated therewith. See Mercer, U.S. Pat. No. 5,914,602, incorporated herein by reference. A common technique is to hook a transmitter to an access point on the utility being traced, such as a water meter, electrical switch box, etc., and to apply thereto an electrical signal of a known alternating current frequency. The utility responds by radiating a magnetic field of the same frequency along its entire length. An operater attempts to follow the path of the underground portion of the utility by detecting the magnetic field with a receiver tuned to the radiated signal. By tuning the magnetic field sensors of the receiver to the imposed frequency, the radiated frequency can be detected to the exclusion of other signals, and the underground portion of the utility can be faithfully traced.
It is also well known that certain utilities are more easily traced using specific frequencies. However, it often occurs that a frequency which was initially effective does not remain so while tracking the utility, due to such variations as its depth below ground level or magnetic radiances in the same bandwidth from other objects or impurities in the ground, which radiances hide or distort the signal. Often, a change in frequency will solve the problem and allow the operator to continue tracing the utility.
At times, the signal disappears or is severely diminished for no apparent reason. Tracing the utility must, of course, cease until the problem is identified and corrected. A great deal of non-productive time results from such problems. It is to the benefit of the operator to be able to quickly determine the cause of the problem and to be able to either solve it or at least to be aware that a prompt solution is not possible.
High among the most common causes of signal loss are battery failure and breaks in the magnetic transmission circuit. The former prevents the magnetic transmitter from supplying an output signal; the latter prevents the signal from being carried by the utility. At present, the operator must return to home base, i.e., the site of the transmitter, to check on the continuity of the circuit, the charge (or lack of charge) of the battery, or to check on the connections between the transmitter and the utility. Currently, it is also necessary for the operator to return to home base to change the frequency of the transmitter to cope with changing conditions. Since it is customary for the operator to walk hundreds of feet away from the transmitter while following the path of the utility, the time wasted travelling to and from the transmitter can be considerable.
Applicants"" invention overcomes these problems by providing a radio link between the receiver and the transmitter which permits the operator to send commands from the receiver to the transmitter which controls selected transmitter functions and which provides the operator with critical information concerning conditions at the transmitter. The combination permits the operator to remain remote from the transmitter while detecting and/or correcting many common problems.
Many prior patents teach radio links between receiver and transmitter, but none, so far as applicants are aware, teach interrogating the transmitter for pertinent information and/or remotely controlling transmitter functions from the receiver. The following patents, incorporated herein by reference, are exemplary.
Yokoi, U.S. Pat. No. 5,194,812, interconnects transmitter and receiver with a radio link, but the RF signal is only a reference frequency to reduce the effects of noise, not a communication link for interrogating and/or controlling the transmitter. Yokoi teaches selecting a detector frequency appropriate for the type of utility to be traced, but does not teach changing that frequency once it has been selected due to events arising during field operations. Yokoi especially does not teach changing the tranmission frequency from the receiver.
Rider, U.S. Pat. No. 5,264,795, establishes communications between an operator at the transmitter and an operator at the receiver by means of a modulated signal induced in the pipe. The use of the induction signal as the communications carrier is inherently less efficient and less reliable than the use of a radio link. Further, Rider teaches communications between people, one at the transmitter and one at the receiver, not between receiver and transmitter per se. Rider continuously sends battery level information from transmitter to receiver without operator intervention, but he does not teach sending battery level information only upon request from a remote operator.
Archambeault et al., U.S. Pat. No. 5,469,155, and Mercer, U.S. Pat. No. 5,698,981, relay drill head signals picked up by a receiver to the operator at the drill control panel. Archambeault et al. use the information to control the drill; Mercer uses the information to record the drill path. Mercer, U.S. Pat. No. 5,914,602, supra, radios signals from pipes or drill heads directly to the drill operator. All require an operator at the transmitter, and none teach controlling tranmitter functions by an operator remotely located with the receiver.
A radio link is established between the portable receiver used by an operator to trace the underground portion of a utility and the transmitter which induces a magnetic signal in the utility. Circuitry in both transmitter and receiver allows the operator to interrogate the transmitter for essential information, such as whether or not the transmitter is generating a signal, the frequency being used in the transmission, the level of the transmitter""s battery, or whether or not a complete transmission circuit is existent. Circuitry is also provided for controlling functions at the transmitter from the receiver carried by an operator remote from the transmitter, such as changing the transmission frequency of the generator, or conserving battery power by switching the transmitter""s frequency generator off during periods of non-use.
It is an object of the invention to provide a utility tracing system which permits operation thereof by only one operator.
It is a further object of the invention to provide a utility tracing system which saves valuable field time by eliminating the need for the operator to repeatedly return to the location of the transmitter to find and/or fix problems.
It is a further object of the invention to provide a utility tracing system which includes a radio link between a receiver and a transmitter capable of allowing an operator to interrogate conditions at the transmitter from the receiver and to control functions of the transmitter from the receiver, while the operator is remote from the transmitter.